One obvious requirement for aircraft safety is to avoid flying into things. There are many possible flight path obstructions most of them having a specific and constant geographic coordinate and height. Obstruction coordinate and height data are contained in databases such as the various geographic information system (GIS) databases used in flight planning and in producing navigation maps for pilots. New obstructions are constantly being produced during and after construction activities and the quicker the new obstructions are added to the databases, the safer air travel is. Furthermore, obstruction location and height should be occasionally verified to correct faulty GIS data.
Object height has been measured in a number of different ways, for example, aerial photograph stereography. In aerial photograph stereography, two pictures are taken. After matching the features between the two pictures, stereographic equations are solved in an attempt to locate the features in a three dimensional space. To measure obstructions, one feature is the obstruction's top and another is the ground at the obstruction's base. The resolution suffers because aerial photographs are taken in a direction which is orthogonal to the measurement of interest. To wit, the camera is looking in the approximately vertical axis, yet seeks to measure vertical size. This means that small errors in the apparent position of vertical objects are magnified geometrically. Also, fine structures such as antennae atop towers or buildings are difficult to detect, yet an aircraft striking one of these small antennae could be damaged or destroyed.
Down-looking LiDAR systems have been used to construct topographic digital terrain maps. This at least makes a direct measure in the vertical, and indeed these systems provide excellent maps of larger topographic hazards to aviation including terrain and buildings. However, the detection of smaller features is a problem. LiDAR systems may be capable of measuring objects as small as a meter across, but cannot hope to measure an antenna of ½ inch diameter. As such, certain common aviation hazards are overlooked.
Perspective photographic measurement techniques use a picture or multiple pictures taken with a camera instrumented to measure line of sight angles. This method has the advantage of looking at the measurement of interest—the obstruction from the side. However, in practice it is not practical to image a building with enough pixel resolution to capture from the base of the building and be able to clearly measure the lightening rod on its top.
The existing methods do not provide a consistent and accurate measurement of the fine structure of obstructions. The fine structures, such as a ½ inch antenna, are quite capable of damaging aircraft. Systems and methods for rapidly, inexpensively, and accurately measuring obstruction heights are needed.